Multibeam particle microscope for reducing particle beam induced marks on samples

Abstract

The present invention relates to a multi-beam particle microscope for reducing particle beam induced marks on a sample in the presence of high voltages, further reducing the generation of residual gas in the sample chamber by using a specially shielded specific objective lens cable and / or a special sample stage cable.

Description

[Technical field]

[0001] The present invention relates to a multi-beam particle microscope for reducing particle beam induced marks on a sample. [Background technology]

[0002] With the continued development of increasingly smaller and more complex microstructures, such as semiconductor components, there is a need to further develop and optimize planar manufacturing techniques and inspection systems for manufacturing and inspecting small dimensions of the microstructures. As an example, the development and manufacture of semiconductor components requires monitoring of the design of test wafers, and planar manufacturing techniques require process optimization for reliable manufacture at high throughput. More recently, there has been a demand for the analysis of semiconductor wafers for reverse engineering and for customer-specific individual configuration of semiconductor components. Thus, there is a need for inspection tools that can be used at high throughput to examine the microstructures on the wafer with high accuracy.

[0003] Typical silicon wafers used in the manufacture of semiconductor components have a diameter of up to 300 mm. Each wafer can be up to 800 mm 2A semiconductor device includes a plurality of semiconductor structures fabricated in layers on the surface of a wafer by planar integration techniques. The semiconductor wafer typically has a flat surface due to the manufacturing process. The feature sizes of the integrated semiconductor structures in this case range from a few μm to 5 nm critical dimension (CD), but in the near future the feature sizes will become even smaller, and in the future the feature sizes or critical dimensions (CD) are expected to be less than 3 nm, e.g., 2 nm, or even less than 1 nm. For these small feature sizes, defects of the size of the critical dimension must be identified quickly over a very large area. For some applications, the specification requirements for the accuracy of the measurements provided by the inspection equipment are even higher, e.g., by a factor of two or an order of magnitude. As an example, the width of the semiconductor features must be measured with an accuracy of less than 1 nm, e.g., 0.3 nm or less, and the relative positions of the semiconductor structures must be determined with an overlay accuracy of less than 1 nm, e.g., 0.3 nm or less.

[0004] The MSEM, or multi-beam scanning electron microscope, is a relatively new development in the field of charged particle systems ("charged particle microscopes (CPM)"). By way of example, multi-beam scanning electron microscopes are disclosed in US Pat. No. 7,244,949 (B2) and US Patent Application Publication No. 2019 / 0355544. In a multi-beam electron microscope or MSEM, a sample is illuminated simultaneously by a number of individual electron beams arranged in a field of view or grid. By way of example, 4-10,000 individual electron beams can be provided as primary radiation, each individual electron beam being spaced apart from the adjacent individual electron beam by a pitch of 1-200 micrometers. By way of example, an MSEM has approximately 100 separate individual electron beams ("beamlets"), which are arranged, for example, in a hexagonal grid, with the individual electron beams being spaced apart by a pitch of approximately 10 μm. A common objective lens focuses the multiple individual charged particle beams (primary beams) onto the surface of the sample to be examined. By way of example, the specimen may be a semiconductor wafer fixed on a wafer holder attached to a movable stage. During irradiation of the wafer surface by the individual primary charged particle beams, interaction products, e.g. secondary electrons or backscattered electrons, arise from the surface of the wafer. Their starting points correspond to those positions on the specimen at which in each case the multiple individual primary particle beams are focused. The amount and energy of the interaction products depend on the material composition and the topography of the wafer surface. The interaction products form multiple individual secondary particle beams (secondary beams), which are collected by a common objective lens and, as a result of the projection imaging system of the multi-beam inspection system, impinge on a detector arranged in a detection plane. The detector comprises multiple detection areas, each of which comprises multiple detection pixels, and the detector captures the intensity distribution for each of the individual secondary particle beams. In this process, an image field of, e.g., 100 μm×100 μm is obtained.

[0005] Prior art multi-beam electron microscopes include a series of electrostatic and magnetic elements. At least some of the electrostatic and magnetic elements are configurable to adapt the focal position and astigmatism of the multiple individual charged particle beams. Furthermore, prior art charged particle multi-beam systems include at least one crossover plane of the individual primary or secondary charged particle beams. Furthermore, prior art systems include a detection system to make adjustments easier. Prior art multi-beam particle microscopes include at least one beam deflector ("deflection scanner") for sweeping an area of ​​the sample surface with multiple individual primary particle beams to obtain an image field of the sample surface. Further details regarding the multi-beam electron microscope and the method of operating it are described in International Patent Application having Application Number WO2021239380, the disclosure of which is incorporated herein by reference in its entirety.

[0006] To be able to carry out an accurate examination of a sample or a sample surface using a multibeam scanning electron microscope, or more generally using a multibeam particle microscope, it is necessary to handle very clean samples in a very clean environment under high vacuum. Contaminants or residual gases in the vacuum that may be introduced onto the sample surface may result in abrupt contrast changes during imaging using a multibeam particle microscope, which may make accurate analysis more difficult or even impossible. In this case, the adsorption of particles on the sample surface may be performed spontaneously or in a particle beam induced manner. In this case, particle beam induced contamination is usually caused by the growth of carbon on the sample surface. A known and safe measure to prevent this contamination is the use of materials in the vacuum chamber that do not or barely emit carbon.

[0007] Nevertheless, experiments carried out by the applicant have shown that even under high vacuum, these measures are not sufficient to sufficiently reduce particle beam induced marks on the sample surface and at the same time are not sufficient in any case given the ever increasing required precision of inspection tasks with multi-beam particle microscopes.

[0008] US 2020 / 0 373 116 discloses a multi-beam electron microscope that can detect backscattered electrons in addition to secondary electrons. For this purpose, a specific membrane is provided between the sample and the lower pole piece of the objective lens.

[0009] US 2020 / 0 243 296 discloses a multi-beam particle microscope having an objective lens including three pole pieces, where electrical insulation is provided between the pole pieces. A shielding electrode is further disclosed to reduce charging of the sample.

[0010] US Patent Application Publication No. 2007 / 0194 230 relates to the inspection of magnetic samples by SPLEEM. Summary of the Invention

[0011] It is therefore an object of the present invention to further improve existing multi-beam particle microscopes. In particular, an object is to provide a multi-beam particle microscope which allows particle-beam induced marks on a sample to be further reduced.

[0012] The object is achieved by the subject matter of the independent patent claims. Advantageous embodiments of the invention are evident from the dependent patent claims.

[0013] This patent application claims priority to German patent application No. 10 2022104 535.8 of February 25, 2022, the disclosure of which is incorporated by reference in its entirety into this patent application.

[0014] The present invention is based on the experiments carried out by the applicant on the occurrence of the described particle beam-induced contaminants or particle beam-induced traces on the sample surface. In this case, it was surprisingly found that there is a further source of contaminants not previously known in the context of multi-beam particle microscopes. In particular, contaminants arise when multi-beam particle microscopes are used in which there are very high voltages or (in the case of negatively charged particles such as electrons) very low voltages at the objective and / or sample stage under vacuum. According to the applicant's results, contaminants arise more and more whenever high electric fields arise in the vacuum chamber with the sample to be examined. The cause of this is internal or corona discharges occurring in the vacuum chamber near the cables. This affects in particular the objective cable and the sample stage cable, which are at very high voltages with respect to their absolute value relative to the grounded vacuum chamber. When discharges occur in the vacuum chamber, atoms or molecules or generally residual gases still present in the vacuum chamber are ionized and accelerated. These ions then collide, for example, with the grounded walls or cables of the vacuum chamber, where they knock out material (sputtering effect), for example from the material of the insulator that typically surrounds the cable. Generally speaking, therefore, due to the internal or corona discharge, the sputtering effect results in a greater amount of disturbing residual material or gas being present in the vacuum chamber than would be present in the absence of the corresponding discharge.

[0015] The present invention exploits these insights. As part of the invention, the occurrence of internal or corona discharges within the vacuum chamber housing the sample is reduced or completely prevented.

[0016] Therefore, according to a first aspect of the invention, the present invention provides a multi-beam particle microscope for reducing particle beam induced marks on a sample, comprising the following features: a multi-beam generator configured to generate a first field of view of a plurality of individual first charged particle beams; a first particle-optical unit having a first particle-optical beam path, the first particle-optical unit configured to image the generated individual particle beams onto a sample surface at an object plane such that the first individual particle beams are incident on the sample surface at incidence positions forming a second field of view; a detection system having a plurality of detection regions forming a third field of view; a second particle-optical unit having a second particle-optical beam path, the second particle-optical unit configured to image second individual particle beams originating from incidence positions in the second field of view into a third field of view of a detection region of the detection system; a magnetic and / or electrostatic objective lens through which both the first individual particle beam and the second individual particle beam pass; a beam switch disposed in a first particle-optical beam path between the multi-beam generator and the objective lens and in a second particle-optical beam path between the objective lens and a detection system; a specimen stage for holding and / or positioning the specimen during specimen inspection; a controller configured to control the multi-beam particle microscope; Equipped with The objective lens and the sample stage are placed in a grounded vacuum chamber. A high voltage can be or is applied to the objective lens by means of an objective lens cable that is guided at least partially inside the vacuum chamber, A high voltage can be or is applied to the sample stage by a sample stage cable that is guided at least partially within the vacuum chamber; the objective lens cable has at least a partial shield in a section guided into the vacuum chamber to reduce electrostatic discharge between the objective lens cable and the vacuum chamber, and / or the sample stage cable has at least a partial shield in a section guided into the vacuum chamber to reduce electrostatic discharge between the sample stage cable and the vacuum chamber; This relates to multi-beam particle microscopes.

[0017] The charged particles can be, for example, electrons, positrons, muons or ions, or other charged particles. Preferably, the charged particles are electrons, for example generated using a thermal field emission source (TFE). However, other particle sources can also be used.

[0018] The individual particle beams are preferably arranged in a lattice arrangement, i.e. the arrangement of the individual particle beams relative to each other is preferably fixed or can be selected.Preferably, this is a regular lattice arrangement, which can provide, in particular, a uniformly spaced, for example, a square, rectangular or hexagonal arrangement of the individual particle beams relative to each other.It is advantageous if the number of the individual particle beams is 3n(n-1)+1, where n is any natural number.

[0019] The multi-beam particle microscope can be a system operating with a single column, but it is also possible that the multi-beam particle microscope is realized by a multi-column system. Preferably, the multi-beam particle microscope comprises only one objective lens (which can also be multi-segmented) through which all the individual particle beams pass. However, it is also possible that multiple objective lenses are provided or that an objective lens array is provided, with only the first individual particle beams or only a subgroup of all the individual particle beams passing through each objective lens (which can also be multi-segmented) of the objective lens array. It is therefore possible that only one objective lens cable is provided for applying a high voltage to the objective lens. However, it is also possible that multiple objective lens cables are provided for applying a high voltage to one or more objective lenses. The fewer objective lens cables required, the better it is to reduce undesired particle beam induced marks on the sample. Therefore, preferably, only one objective lens cable is provided.

[0020] The sample stage serves to hold and / or position the sample during inspection. A high voltage is applied to the sample stage, so that the sample that can be or is placed on the sample stage is also at the same potential. For this reason, preferably only one sample stage cable is used, although it is also possible to provide multiple sample stage cables.

[0021] In the following all references to the objective lens cable and the sample stage cable will be made in the singular, but it will be appreciated that multiple cables having the characteristics described below may be provided in each case.

[0022] The objective lens cable and the sample stage cable are guided at least partially in the vacuum chamber. Therefore, if a correspondingly high electric field is present, in these sections the above-described internal or corona discharges could occur. Therefore, the sections are at least partially provided with a shield, which prevents discharges. At least partially means two different things here: firstly, the shield does not have to be provided along the entire section that extends into the vacuum chamber (but can be provided), and secondly, the cable shield does not have to completely surround or enclose or cover the surface of the cable 100% at every point thereof (but can be).

[0023] The shield itself in this case is a shield that is known per se and can be realized in various ways. The way in which the shield is realized can be the same for the objective cable and for the sample stage cable, but can also be different. What is important in principle is the electrical conductivity of the shield and a sufficiently good containment of the electric field by the shield according to the principle of the Faraday cage.

[0024] According to one preferred embodiment of the invention, the length of the shielding of the objective cable is at least 20 cm and / or the length of the shielding of the sample stage cable is at least 40 cm, so that the shielding is in each case effective over at least this entire length, which also applies if the shielding is provided in such a way that it does not cover the cable 100%.

[0025] According to one preferred embodiment of the present invention, the vacuum that can be generated or is generated in the vacuum chamber is 10 -7 mbar or better (hence the lower pressure). Preferably, the total pressure in the vacuum chamber is ≦10 -8 mbar, most preferably around 10 -9 mbar. These values ​​relate to the situation where high voltages are present at the objective and sample stage. The effect of shielding the objective and sample stage cables is very large even in the case of the already inherently very low total pressures mentioned above. This is noteworthy: the pressure (more precisely, the partial pressure) of certain elements in the vacuum chamber can be reduced by approximately a factor of 10 by cable shielding in the objective and sample stage cables.

[0026] Additionally or alternatively, the absolute value of the voltage that can be or is applied to the objective lens and / or the sample stage is at least 15 kV, in particular at least 20 kV or in particular at least 30 kV. In the case of these high voltages or voltage differences with respect to the vacuum chamber (earth potential), even in high vacuum, the described discharges occur. The objective lens is generally positioned immediately upstream of the sample or sample stage, so that approximately the same potential exists at the objective lens and the sample, for example, in each case approximately ±20 kV, ±22 kV, ±25 kV, ±28 kV, ±30 kV or ±32 kV.

[0027] According to one preferred embodiment of the invention, the objective cable and / or the sample stage cable include an insulation around the core of the respective cable. In this case, the cable is preferably a single-core cable, but can also be a multi-core cable. In this case, the shield is arranged respectively on the outside with respect to the insulation. Objective cables and sample stage cables already according to the prior art typically have insulation whose material has only a low level of outgassing. It is therefore noted at this point that the theoretical omission of the insulation, although it would solve the problem of outgassing, does not solve the problem addressed by the present invention, regarding internal or corona discharges in the residual gas and the associated generation and acceleration of ions of the residual gas, which leads to increased detachment or knocking out of particles in the area of ​​the cable or on the wall of the vacuum chamber. Therefore, the already known insulation can also be maintained in combination with the shield according to the invention.

[0028] According to one preferred embodiment of the invention, the insulation comprises a plastic that is hydrophobic, has a low level of outgassing, and / or is elastic. The elasticity allows for cable flexibility along with the cable insulation. Outgassing rates for plastics are often specified as TML ("total mass loss") or CVCM ("collected volatile condensable matter"). Total mass loss is the percentage of mass lost after a sample is heated to 125°C for 24 hours under vacuum. CVCM is the fraction of mass that condenses on a nearby test surface at 25°C. TML and CVCM can be used to compare various materials with respect to their suitability for use in vacuum. Outgassing rates can be determined and expressed as (volume times pressure) per unit area per unit time to predict the actual pressure that will be achieved in the system or to calculate the suction volume required to reach a desired pressure. Low levels of outgassing within the meaning of this patent application are defined as follows: TML≦1%, CVMC≦0.02, outgassing rate≦10 -7 torr * litre / cm 2*It exists if at least one of s is satisfied.

[0029] According to one preferred embodiment of the invention, the plastic is selected from at least one of the following groups of plastics: polyimide, polyethylene, polypropylene, polytetrafluoroethylene, fluorinated ethylene propylene, perfluoroalkoxyalkanes.

[0030] According to one preferred embodiment of the invention, the shielding of the objective cable and / or the sample stage cable is electrically conductive and free of organic materials, in particular free of fluoro-organic materials. Metals and / or metalloids and their alloys are therefore in principle suitable as shielding due to their electrical conductivity. The metals preferably used are copper, aluminum and / or silver, but other metals can also be used. It is preferable to dispense with organic materials, in particular fluoro-organic materials, since carbon can adsorb, in particular substantially and therefore disruptively, on the sample surface or be deposited there in a particle beam-induced manner.

[0031] According to one preferred embodiment of the invention, the shielding comprises a braided shield. By way of example, the shielding can be braided from bare or tinned copper wire, with the tinned embodiment having significantly better properties against corrosion. The advantages of a braided shield are very good attenuation and good mechanical properties. At a certain braid angle, a very flexible line is created with approximately 70% linear and 90% optical coverage, which avoids tension on the shielding wire. However, other embodiment variations are possible. However, other embodiment variations are possible.

[0032] Additionally or alternatively, the shielding may include a twisted shield. The coverage of the inner conductor generally ranges between 95% and 100%. By way of example, a shield made of bare or tinned copper wire is placed or wrapped around the inner conductor(s), with tinned embodiments having significantly better properties against corrosion. An advantage of twisted shields is their simple, fast, and inexpensive manufacture. As an alternative to copper, other metals may be used, such as aluminum or silver.

[0033] Additionally or alternatively, it is also possible for the shield to comprise a foil, in particular an aluminum foil. It is possible for the foil to be coated with aluminum. Preferably, the foil provides 100% coverage, but it can also have cutouts and / or holes without its functionality being significantly impaired.

[0034] According to one preferred embodiment of the invention, the shielding is applied to the cable, in particular to the cable insulation, by vapor deposition (e.g. electron beam evaporation, resistive evaporation or generally physical vapor deposition (PVD)). Preferably, the coverage is complete, i.e. 100%. For the thickness Sd of the layer produced by vapor deposition, preferably 10 nm≦Sd≦200 nm applies, for example 10 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm or 200 μm. In this case, good adhesion of the applied substance to the cable or to the insulation is important, which of course depends on the combination of materials used respectively, as known to the person skilled in the relevant art.

[0035] According to one preferred embodiment of the invention, the shield applied by vapor deposition comprises at least one metal from the following group of metals: platinum, palladium, copper, titanium, aluminum, gold, silver, chromium, tantalum, tungsten, molybdenum.

[0036] Additionally or alternatively, according to a further preferred embodiment, the shield applied by deposition comprises at least one semi-metal from the following group of metalloids: Si, Si / Ge, GaAs, AlAs, InAs, GaP, InP, InSb, GaSb, GaN, AlN, InN, ZnSe, ZnS, CdTe.

[0037] The above-mentioned embodiments of the present invention can be fully or partially combined with each other, provided that no technical contradictions result.

[0038] Of course, it is also possible to shield one or more further cables in a similar manner to the shielding of the objective lens cable and the shielding of the sample stage cable.

[0039] The present invention may be better understood with reference to the accompanying drawings. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 shows a schematic diagram of a multi-beam particle microscope (MSEM). [Diagram 2] FIG. 1 is a schematic cross-sectional view of a multi-beam particle microscope. [Diagram 3] FIG. 2 shows the measurement of the partial pressure of residual gases in a high vacuum. [Figure 4] FIG. 1 shows a schematic diagram of a vacuum chamber of a multi-beam particle microscope with objective lens cables and sample stage cables. [Diagram 5] FIG. 1 shows a schematic diagram of a) the effect of corona discharge in a vacuum chamber and b) prevention of corona discharge in a vacuum chamber by a shield. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] FIG. 1 is a schematic diagram of a particle beam system 1 in the form of a multi-beam particle microscope 1 using multiple particle beams. The particle beam system 1 generates multiple particle beams that are incident on an object to be examined in order to generate there interaction products, e.g. secondary electrons, which originate from the object and are subsequently detected. The particle beam system 1 is of the scanning electron microscope (SEM) type and uses multiple primary particle beams 3 that are incident on the surface of the object 7 at multiple positions 5 and generate there multiple electron beam spots, or spots, spatially separated from one another. The object 7 to be examined can be of any desired type, e.g. a semiconductor wafer or a biological sample, and can include an array of small elements or the like. The surface of the object 7 is arranged at a first surface 101 (object surface) of an objective lens 102 of the objective lens system 100.

[0042] Enlarged detail l1 in Fig. 1 shows a plan view of an object plane 101 with a regular square field 103 of 5 incidence positions formed in the first plane 101. In Fig. 1 the number of incidence positions is 25 forming a 5 x 5 field 103. The number of incidence positions 25 is a number chosen for the sake of simplicity of the drawing. In practice the number of beams and therefore the number of incidence positions can be chosen to be significantly larger, for example 20 x 30, 100 x 100, etc.

[0043] In the illustrated embodiment, the field of view 103 of the entrance locations 5 is a generally square field of view with a constant spacing P1 between adjacent entrance locations. Exemplary values ​​for spacing P1 are 1 micrometer, 10 micrometers, and 40 micrometers. However, it is also possible for the field of view 103 to have other symmetries, such as, for example, hexagonal symmetry.

[0044] The diameter of the beam spot formed in the first surface 101 can be small. Exemplary values ​​of this diameter are 1 nanometer, 5 nanometers, 10 nanometers, 100 nanometers and 200 nanometers. The focusing of the particle beam 3 to form the beam spot 5 is performed by the objective lens system 100.

[0045] Primary particles incident on the object generate interaction products, e.g. secondary electrons, backscattered electrons or primary particles whose motion has been reversed for other reasons, which originate from the surface of the object 7 or from the first surface 101. The interaction products originating from the surface of the object 7 are shaped by the objective lens 102 to form a secondary particle beam 9. The particle beam system 1 provides a particle beam path 11 for directing a plurality of secondary particle beams 9 to a detector system 200. The detector system 200 includes a particle optical unit with a projection lens 205 for directing the secondary particle beams 9 to a particle multi-detector 209.

[0046] Detail l2 in Fig. 1 shows a plan view of a plane 211 in which the individual detection areas of the particle multi-detector 209 are located, where the secondary particle beam 9 is incident at positions 213. The incident positions 213 are in the field of view 217 at equal spacings P2 from each other. Exemplary values ​​for spacing P2 are 10 micrometers, 100 micrometers and 200 micrometers.

[0047] The primary particle beam 3 is generated in a beam generating device 300 comprising at least one particle source 301 (e.g. an electron source), at least one collimation lens 303, a multi-aperture arrangement 305 and a field lens 307. The particle source 301 generates a diverging particle beam 309, which is collimated or at least substantially collimated by the collimation lens 303 to shape a beam 311 that illuminates the multi-aperture arrangement 305.

[0048] Detail l3 in FIG. 1 shows a plan view of a multi-aperture configuration 305. The multi-aperture configuration 305 includes a multi-aperture plate 313 in which a plurality of openings or apertures 315 are formed. Midpoints 317 of the openings 315 are located within a field of view 319 imaged to a field of view 103 formed by a beam spot 5 at the object plane 101. The spacing P3 between the midpoints 317 of the apertures 315 can have exemplary values ​​of 5 micrometers, 100 micrometers and 200 micrometers. The diameter D of the apertures 315 is smaller than the distance P3 between the midpoints of the apertures. Exemplary values ​​of the diameter D are 0.2×P3, 0.4×P3 and 0.8×P3.

[0049] Particles of the illumination particle beam 311 pass through the aperture 315 and form the particle beam 3. Particles of the illumination beam 311 that are incident on the plate 313 are absorbed by the plate 313 and do not contribute to the formation of the particle beam 3.

[0050] Due to the applied electrostatic field, the multi-aperture arrangement 305 focuses each of the particle beams 3 such that a beam focus 323 is formed in a plane 325. Alternatively, the beam focus 323 may be virtual. The diameter of the beam focus 323 may be, for example, 10 nanometers, 100 nanometers and 1 micrometer.

[0051] The field lens 307 and the objective lens 102 provide a first imaging particle-optical unit for imaging a plane 325, where the beam focus 323 is formed, onto a first plane 101, so that a field 103 of incidence positions 5 or beam spots arise therein. If the surface of the object 7 is located in the first plane, a beam spot is correspondingly formed on the objective surface.

[0052] The objective lens 102 and the projection lens arrangement 205 provide a second imaging particle-optical unit for imaging the first plane 101 onto the detection plane 211. The objective lens 102 is thus a lens that is part of both the first and the second particle-optical unit, whereas the field lens 307 belongs only to the first particle-optical unit and the projection lens 205 belongs only to the second particle-optical unit.

[0053] A beam switch 400 is arranged in the beam path of the first particle-optical unit between the multi-aperture arrangement 305 and the objective system 100. The beam switch 400 is also part of the second particle-optical unit in the beam path between the objective system 100 and the detector system 200.

[0054] Further information on such multi-beam particle beam systems and components used therein, such as, for example, particle sources, multi-aperture plates and lenses, can be taken from international patent applications WO 2005 / 024881, WO 2007 / 028595, WO 2007 / 028596, WO 2011 / 124352 and WO 2007 / 060017, and German patent applications DE 10 2013 016 113 A1 and DE 10 2013 014 976 A1, the disclosures of which are incorporated in their entirety into the present application by reference.

[0055] The multi-particle beam system 1 further comprises a computer system 10 configured for controlling the individual particle-optical components of the multi-particle beam system and for evaluating and analysing the signals obtained by the multi-detector 209. The computer system 10 may consist of a number of individual computers or components. A multi-beam particle beam system in the form of a multi-beam particle microscope 1 may comprise cable shields according to the invention for the objective lens cable and the sample stage cable.

[0056] FIG. 2 shows a schematic cross-sectional view of a multi-particle beam system, for example the multi-beam particle microscope shown in FIG. 1. In this case, FIG. 2 mainly shows a particle-optical beam path under vacuum as an example. The multi-beam particle microscope 1 according to the example shown in FIG. 2 again firstly comprises a particle source 301. In the example shown, this particle source 301 emits individual particle beams, which contain charged particles, for example electrons. In this case, the particle source 301 can be operated at high voltage, for example at least ±20 kV or ±30 kV. In FIG. 2, the particle beam or the particle-optical beam path is shown diagrammatically by a dashed line with the reference number 3. The individual particle beams 3 first pass through a condenser lens system 303 and then enter a multi-aperture arrangement 305. This multi-aperture arrangement 305, possibly with further particle-optical components, serves as a multi-beam generator. The multi-beam generator is preferably at approximately ground potential. The first particle beam emerging from the multi-aperture arrangement 305 then passes through a field lens or field lens system 307 and then enters the beam switch 400. After passing through the beam switch 400, the first particle beam 3 passes through a scanning deflector 500 and immediately afterwards the particle-optical objective lens 102 before impinging on the object 7. As a result of this impingement, secondary particles are emitted from the object 7, for example secondary electrons. These secondary particles form a second particle beam, to which a second particle-optical beam path 9 is assigned. After emerging from the object 7, the second particle beam first passes through the particle-optical objective lens 102 and then through the scanning deflector 500 before entering the beam switch 400. The second particle beam 9 then leaves the beam switch 400, passes through the projection lens system 205, passes through the electrostatic element 260 and then impinges on the particle-optical detector unit 209.

[0057] The particle beam 3, 9 passes through a beam tube 460 which is evacuated. In some regions, the beam tube 460 widens to form larger chambers or is interrupted by chambers. These chambers include, for example, the chamber 350 in the region of the particle source 301, the chamber 355 in the region of the multi-aperture arrangement 305 of a particle-optical component, for example the multi-beam generator or the multi-aperture arrangement 305, the chamber 250 in the region of the detection system 209, and also the vacuum chamber 150 in the region of the objective lens 102 and the sample stage 153 with the sample 7. In this case, inside the beam tube 460 in the beam switch 400, the chamber 10 -5 Less than mbar, especially 10 -7 mbar and / or 10 -9 A high vacuum, preferably having a pressure of less than 1000 mbar, prevails. In each case, in the already mentioned chambers 350, 355 and 250, 10 -5 Less than mbar, especially 10 -7 mbar and / or 10 -9 A vacuum, preferably having a pressure of less than mbar, prevails. In a vacuum chamber 150 containing the objective lens 102 and a sample stage 153 with a sample 7, -7 Less than mbar, especially 10 -8 mbar and / or 10 -9 Preferably, a vacuum prevails having a total pressure of less than mbar.

[0058] The objective lens 102 has an upper pole piece 108 and a lower pole piece 109. A winding 110 for generating a magnetic field is positioned between the two pole pieces 108 and 109. In this case, the upper pole piece 108 and the lower pole piece 109 can be electrically insulated from each other. In the illustrated example, the particle-optical objective lens 102 is a magnetic lens, but it can also be an electrostatic lens or a combined magnetic / electrostatic lens. In this case, the objective lens is operated with a high voltage, i.e. with a voltage that is at least 20 kV, in particular at least 30 kV, in terms of absolute value, in the illustrated example. The voltage can be, for example, approximately ±20 kV, ±22 kV, ±25 kV, ±28 kV, ±30 kV or ±32 kV. Both the objective lens 102 and the sample stage 153 or sample 7 are in close proximity, so the voltage present at the sample stage 153 or sample 7 is also a high voltage, of the same order of magnitude as at the objective lens 102. An objective lens cable 151 and a sample stage cable 152, respectively, are used to apply the voltage (neither of which are shown in FIG. 2 for reasons of simplicity).

[0059] Due to the use of high voltages the already described multi-beam particle microscope 1 differs from many other particle microscopes according to the prior art, in which the sample 7 is at ground potential. However, it only became apparent upon detailed investigation by the applicant that this difference is significant with regard to particle-beam or electron-beam induced marks on the sample 7 despite the high vacuum in the region of the sample 7.

[0060] FIG. 3 shows the measurement of partial pressure of residual gases in high vacuum. Specifically, the applicant investigated the partial pressure of various elements or various residual gases in the vacuum chamber 150. A mass spectrometer was used to determine the partial pressure. In the example shown in FIG. 3, two curves are plotted, in one curve shown by the open dots, the partial pressure of substances having atomic masses 101-200 is plotted, and in the curve shown by the filled circles, the partial pressure of substances having atomic masses 45-100 is plotted. In this case, each partial pressure is plotted against time.

[0061] The partial pressure measurements were started in each case without a magnetic field, i.e. during time interval T1 both the vacuum chamber 150 and the objective lens 102 and the sample stage 153 were grounded, i.e. no voltage was present there (i.e. during this time interval T1 no imaging with the multibeam particle microscope was taking place, otherwise a voltage or high voltage would have had to be applied or present at the objective lens 102 and the sample stage 153. No imaging was taking place during either time interval T2 or T3). The respective partial pressures were approximately constant during time interval T1, each approximately 2×10 -10 mbar and approximately 8×10 -10mbar. After one hour, a high voltage, which in the illustrated example is approximately -30 kV, was applied to both the objective cable 151 and the sample stage cable 152. Immediately after application of the high voltage, a jump of approximately an order of magnitude in the respective partial pressure was observed in each case. Then, during the time interval T2, during which the high voltage is applied, the partial pressure again remains approximately constant in each case. Then, in the time interval T3, the high voltage was switched off again, i.e. the two cables 151, 152 were grounded. Shortly thereafter, the partial pressure was restored again, i.e. it slowly decreased. The recovery was not sudden, but rather took place gradually. What can be initially deduced from this is that the generation of residual gas is voltage-induced or due to a corona discharge between the cables 151, 152, on the one hand, and the grounded wall 159 of the vacuum chamber 150, on the other hand. Disturbance of the mass spectrometer by the high voltage carried by the cables can be made unlikely since the reduction in partial pressure after the high voltage is switched off is gradual rather than abrupt. In this case, the residual gas measured when the high voltage is present during time interval T2 results from the sputtering effect explained above. When a discharge occurs in the vacuum chamber 150, the residual gas still present in the vacuum chamber 150 is ionized and the ions are accelerated according to their charge. The ions then collide, for example, with the grounded wall 159 of the vacuum chamber 150 or with the cables 151, 152, knocking out material, in particular from the insulator 158 surrounding the cables 151, 152, which then moves freely within the vacuum chamber 150 and contributes to the residual gas therein.

[0062] FIG. 4 shows diagrammatically the vacuum chamber 150 of the multi-beam particle microscope 1 with an objective lens cable 151 and a sample stage cable 152. The sample stage 153 serves to hold and / or position the sample 7 during sample inspection. The structure of the sample stage 153 is shown only diagrammatically as a whole, the example shown relates to a sample stage 153 that is adjustable in the z-direction, i.e. height adjustable. A cable 152 is connected to the sample stage surface 154 of this sample stage, to which a high voltage can be or is applied. The objective lens 102 is positioned directly above the sample stage surface 154, the objective lens 102 being only shown very diagrammatically in FIG. 4. The objective lens cable 151 is connected to the objective lens 102. In the example shown, both cables 151, 152 are insulated or surrounded by an insulator 158. The insulator 158 may, for example, comprise polyimide, which has a low level of outgassing and is elastic according to the required flexibility of the cables 151, 152. However, other materials are possible. In the illustrated example, both cables 151, 152 are shielded over the entire length that the two cables 151, 152 extend into the vacuum chamber 150. These cables are guided into the chamber 150 via vacuum-compatible and high-voltage compatible connectors 155 and 156, respectively. The length of the objective cable in the vacuum chamber 150, i.e. the length of the shielded section of the objective cable 151, is at least 20 cm in the illustrated example. The length of the shield of the sample stage cable 152 is at least 40 cm in the illustrated example. Of course, the specific length of the respective cables 151, 152 also depends on the design of the vacuum chamber 150.

[0063] In the illustrated example, the vacuum that can be or is generated within the vacuum chamber 150 is 10 -7mbar or better, this specification relating to the total pressure of the residual gas. The absolute value of the voltage that can be or is applied to the objective lens 102 and / or to the sample stage 153 or its surface 154 is at least 20 kV, in particular at least 30 kV. Since electrons are used as the charged particle beam in the illustrated example, the voltage is approximately -30 kV in the illustrated example.

[0064] FIG. 5 illustrates a) the effect of corona discharge within a vacuum chamber 150 and b) the prevention of corona discharge within the vacuum chamber 150 by a shield according to the present invention.

[0065] In this case, a corona discharge according to FIG. 5a) occurs as follows: the cable 151, 152 comprises a conductive core 157 and an insulation 158 arranged therearound. This preferably comprises an insulation made of a plastic that is hydrophobic, has a low level of outgassing and / or is elastic. In this case, the plastic may be selected from at least one of the following plastic groups: polyimide, polyethylene, polypropylene, polytetrafluoroethylene, fluorinated ethylene propylene, perfluoroalkoxyalkanes. However, other plastics may also be used.

[0066] The cables 151, 152 also extend at least partially near the wall 159 of the vacuum chamber 150, which is grounded. A strong electric field is generated between the core 157 of the cables 151, 152 and the wall 159, the field lines of which are shown in FIG. 5a by lines or arrows 161. The high electric field strength between the core 157 and the wall 159 therefore leads to a corona discharge, during which the residual gas present in the vacuum chamber 150 is ionized. Thus, positively and negatively charged ions are shown diagrammatically in FIG. 5a). In the illustrated example, the negatively charged ions move with high speed towards the wall 159 and, when colliding with the wall 159, eject particles from the wall 159. This is indicated by arrows 163. The ejected particles form further residual gas, which can be detected or measured in the vacuum chamber 150. In contrast, in the illustrated example (e.g., potential of core 157 at -30 kV), positively charged ions travel at high speed towards insulator 158 and upon colliding with insulator 158 knock material out of insulator 158, as indicated by arrows 162. These particles then also form additional residual gas within vacuum chamber 150.

[0067] 5b) then shows the situation with the presence of a shield 160 according to the invention, which confines the electric field of the conductive cores 157 of the cables 151, 152 within the shield. There is no longer any potential difference between the shield 160, which is at ground potential, and the wall 159 of the vacuum chamber 150. In this way, corona discharges are avoided and there is no further residual gas formation in the vacuum chamber 150. The formation of particle-beam-induced or electron-beam-induced marks on the sample surface can therefore also be reduced.

[0068] The shield 160 of the objective cable 151 and / or the sample stage cable 152 is electrically conductive and, in the example shown, is free of organic materials, in particular free of fluoro-organic materials. In this case, the shield itself can be realized in various ways, identically or differently for the objective cable 151 and the sample stage cable 152. According to one example, the shield 160 comprises a braided shield. In this case, the shield can be braided from bare copper wire or tinned copper wire, the tinned embodiment having significantly better properties against corrosion. The braided shield has very good attenuation and good mechanical properties. At a certain braiding angle, a very flexible line is created with a linear and optical coverage of approximately 70% and 90%, respectively, which avoids tension on the shielding wire of the shield 160. However, other embodiment variants are also possible.

[0069] Additionally or alternatively, the shield 160 can include a twisted shield. The coverage of the inner conductor or cable including the core 157 and preferably the insulation 158 generally ranges between 95% and 100%. In the case of the twisted shield described, a shield made of bare or tinned copper wires or wires made of some other material, such as aluminum or silver, is placed or wrapped around the cable.

[0070] Additionally or alternatively, it is also possible for the shield 160 to comprise a foil, in particular an aluminum foil. It is also possible for the foil to be coated with aluminum. Preferably, in that case, the foil provides 100% coverage, but can also have cutouts and / or holes, without its functionality being significantly impaired.

[0071] According to one preferred embodiment of the invention, the shield 160 is applied by deposition to the objective cable 151 and / or the sample stage cable 152, in particular to the insulation of the respective cables 151, 152. For this, for example, electron beam evaporation or resistance evaporation can be used, but generally physical vapor deposition (PVD) is also possible. Preferably, the coverage by deposition is complete, i.e. 100%. As a result of the deposition, typical layer thicknesses Sd are 10 nm≦Sd≦200 nm, for example 10 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm or 200 μm. In this case, good adhesion of the applied material by deposition to the cables 151, 152 or to the insulation 158 as the outermost layer of the cables 151, 152 is important, which of course depends on the combination of materials used respectively, as known to those skilled in the relevant art. By way of example, the shield 160 applied by deposition can include at least one metal from the following metal group: platinum, palladium, copper, titanium, aluminum, gold, silver, chromium, tantalum, tungsten, molybdenum. Additionally or alternatively, the shield 160 applied by deposition can include at least one metalloid from the following metalloid group: Si, Si / Ge, GaAs, AlAs, InAs, GaP, InP, InSb, GaSb, GaN, AlN, InN, ZnSe, ZnS, CdTe.

[0072] Thanks to the invention it is now possible to further reduce particle beam induced marks on the sample 7 and thus enable even better recording by the multibeam particle microscope 1 . [Explanation of symbols]

[0073] 1. Multibeam Particle Microscope 3 Primary particle beams (individual particle beams) 5 Beam spot, incident position 7 Object 9 Secondary particle beams (individual particle beams) 10 Computer system, controller 11 Secondary particle beam path 13 Primary Particle Beam Path 25 Sample surface, wafer surface 100 Objective lens system 101 Objective surface 102 Objective Lens 103 Field of view 108 Upper pole piece 109 Lower pole piece 150 Vacuum Chamber 151 Objective lens cable 152 Sample stage cable 153 Sample stage, stage 154 Sample stage surface, stage surface 155 High Vacuum Bushing 156 High Vacuum Bushing 157 Cable Core 158 Insulators 159 Vacuum chamber wall 160 Shield 161 Electric Field Lines 162 Arrows showing sputtering effect 163 Arrows showing sputtering effect 200 Detector System 205 Projection Lens 209 Particle Multi-Detector 211 Detection surface 213 Incident position 215 Detection Area 217 Field of View 250 Vacuum Chamber 300 Beam Generator 301 Particle source 303 Collimation Lens System 305 Multi-aperture configuration, multi-beam generator 306 Micro Optics 307 Field of view lens 309 Diverging Particle Beam 311 Radiation Particle Beam 313 Multi-aperture plate 315 Multi-aperture plate aperture 317 Midpoint of Opening 319 Field of view 323 Beam Focus 325 Intermediate image plane 350 Vacuum Chamber 355 Vacuum Chamber 400 Beam Switch 410 Magnetic Sector 420 Magnetic Sector 460 Beam tube configuration 500 scanning deflector

Claims

1. A multi-beam particle microscope for reducing particle beam induced marks on a sample, comprising the following features: a multi-beam generator configured to generate a first field of a plurality of individual first charged particle beams; a first particle-optical unit having a first particle-optical beam path, the first particle-optical unit configured to image the generated individual particle beams onto the sample surface at an object plane such that the first individual particle beams are incident on the sample surface at incidence positions forming a second field of view; a detection system having a plurality of detection regions forming a third field of view; a second particle-optical unit having a second particle-optical beam path, the second particle-optical unit being configured to image second individual particle beams originating from the incidence positions in the second field of view into the third field of view of the detection area of ​​the detection system; a magnetic and / or electrostatic objective lens through which both the first individual particle beam and the second individual particle beam pass; a beam switch disposed in the first particle-optical beam path between the multi-beam generator and the objective lens and in the second particle-optical beam path between the objective lens and the detection system; a sample stage for holding and / or positioning the sample during sample inspection; a controller configured to control the multi-beam particle microscope; Equipped with the objective lens and the sample stage are disposed in a grounded vacuum chamber; A high voltage can be or is applied to the objective lens by means of an objective lens cable that is guided at least partially inside the vacuum chamber, A high voltage can be or is applied to the sample stage by a sample stage cable that is guided at least partially within the vacuum chamber, the objective lens cable has at least a partial shield in a section guided into the vacuum chamber to reduce electrostatic discharge between the objective lens cable and the vacuum chamber, and / or the sample stage cable has at least a partial shield in a section guided into the vacuum chamber to reduce electrostatic discharge between the sample stage cable and the vacuum chamber. Multibeam particle microscope.

2. 2. The multi-beam particle microscope of claim 1, wherein the objective lens cable includes a shield over the section that is guided into the vacuum chamber and / or the sample stage cable includes a shield over the section that is guided into the vacuum chamber.

3. 3. A multi-beam particle microscope according to claim 1 or 2, wherein the length of the shield of the objective lens cable is at least 20 cm and / or the length of the shield of the sample stage cable is at least 40 cm.

4. The vacuum that can be generated or is generated in the vacuum chamber is 10 -7 mbar or better, and / or 4. The multibeam particle microscope according to claim 1, wherein the absolute value of the voltage that can be or is applied to the objective lens and / or the sample stage is at least 15 kV, in particular at least 20 kV or at least 30 kV.

5. 5. A multi-beam particle microscope as claimed in claim 1, wherein the objective lens cable and / or the sample stage cable include insulation around a core of the cable, and the shield is positioned externally relative to the insulation.

6. 6. The multi-beam particle microscope of claim 5, wherein the insulator comprises a plastic that has a low level of outgassing, is hydrophobic, and / or is elastic.

7. 7. A multi-beam particle microscope according to claim 6, wherein the plastic is selected from at least one of the following group of plastics: polyimide, polyethylene, polypropylene, polytetrafluoroethylene, fluorinated ethylene propylene, perfluoroalkoxyalkanes.

8. The multibeam particle microscope according to any one of claims 1 to 7, wherein the shield of the objective cable and / or the shield of the sample stage cable are electrically conductive and free of organic materials, in particular free of fluoro-organic materials.

9. The multi-beam particle microscope of any one of claims 1 to 8, wherein the shield comprises a braided shield.

10. The multi-beam particle microscope of any one of claims 1 to 9, wherein the shield comprises a twisted shield.

11. A multibeam particle microscope according to any one of the preceding claims, wherein the shield comprises a foil, in particular an aluminium foil.

12. A multibeam particle microscope according to any of the preceding claims, in particular claim 5, wherein the shielding is applied to the cable, in particular to the insulation, by vapor deposition.

13. 13. A multi-beam particle microscope according to claim 12, wherein the shield applied by vapor deposition comprises at least one metal from the following group of metals: platinum, palladium, copper, titanium, aluminium, gold, silver, chromium, tantalum, tungsten, molybdenum.

14. 14. A multi-beam particle microscope according to claim 12 or 13, wherein the shield applied by evaporation comprises at least one metalloid from the following group of metalloids: Si, Si / Ge, GaAs, AlAs, InAs, GaP, InP, InSb, GaSb, GaN, AlN, InN, ZnSe, ZnS, CdTe.

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